Wet spinning of cellulose acetate



v Patented-Feb. i5,

:su'sss will srnmmc or cmnmss scs'rs'rs 'Iraneisl Alles, Waynesboro, Va,alalgnor to lldal'ontdeNemoursacom PATE T OFFICE ton, Del, a eorllration of Delaware No Drawing. Application August 7, 1941,

' Serial N- 4.5,88'l

'3 Claims. (cl. 18-54) a ing not more than 15% by weight or water, basedThis invention relates to the spinning of cellulose acetate nla'ments,and more particularly tothe wet spinning. of acetone-soluble celluloseacetate directly from the gum stag A number of methods have heretoforebeen 5 proposed for forming iiiam'ents of cellulose ace-- I tate'bydirectly extruding the gum (i. e., the acetic. acid-solution ofcellulose acetate produced in the customary acetylation processes)through suitable orifices and into a coas tlng bath where y to form thefilament. Certain of these proposed methodsare restricted to thespinning of pri-' mary or chloroform-soluble cellulose acetate asopposed to secondary or acetone-soluble cellulose acetate universallyemployed in the present dryis spinning methods -of yarn manufacture.Yarn.

made from primary cellulose acetate, however, is. interior to yarn madelrom the secondary cellulose acetate for tliereasons that it'is lessstable cannot be dyed satisfactorily with existing dyes.

The product of these methods cannot therefore successfully compete withdry-spun yarn.

The proposed methods which do relate to the wet spinning ofacetone-soluble cellulose acetate as likewise havenct achievedcommercial success. In many instances, commercial failure may be laid toinherent deficiencies in the coa ulating bath. The deficiency may be inthe lack of essential economy in material and operating .costs, or

it may be in the" coagulating action itself for not all coagulants forcellulose acetate are suit-:

able in'the of acetone-soluble cellulose acetate.- For example,iammonium-sulfate and ammonium chloride, which are known to becoagulantsfor acetone-soluble cellulose acetate, and which have actuallybeen disclosed heretofore in the spinning of chloroform soluble cellu-'lose acetate, are wholly unsatisfactory in the. spinning ofacetone-soluble cellulose acetate be- 40 cause the yarns producedtherefrom are full of stuck filaments and are harsh and wiry to the feeland chalky in appearance; An object of my invention,"therefore, is to onthe total weight of the solution, into an aqueous coagulating solutioncomprising not more than 15% by weight of acetic acid and not more than25% by weight of an salt of an acid of the group consisting of formic,acetic, and nitric acids. The coagulating solution is maintained ata'temperature of from about 3 C. v to about 12 C. The yarn is withdrawnfrom the coagulating solution and is subjected to the usual steps ofwinding, washing, stretching, etc. The following general procedure ispreferred "in carrying out my'invention: Cellulose acetate gum preparedby the esteriflcation of cotton linters and hydrolyzed to obtain thedesired percentage of combined acetic acid, is treated with a salt ofaceticacid, for instance sodium acetate,

to neutralize or render ineflective the sulfuric xacld catalyst andthereby arrest further hydrolyto hydrolysis. it is inherently morebrittle, and it 20' sis. The gum is then filtered to remove anyundissolved material and stored in suitable tanks for a suflicientlength of time to allow the air enis immersed just below the suriace ofthe coagulating bath in such a way as to permit the fllaments to be spunhorizontally. After passlng through a suitable guide, the yarn iswithdrawn from the coagulating bath by means of positively driven rolls.The yarn may be collected on a bobbin, in a centrifugal bucket ordropped into a slowly revolving can, or the acid yarn may he cut intostaple lengths and processed on a conveyor belt. The yarn may be washedin the form collected or withdrawn and: washed in a countercurrentsystem as a rope-or thread. The acidic washwater emuent is preferablysent to an extraction column for recovery.

that there is not an excessive increase in acid concentration near theface of the spinneret.

The coagulating solution is circulated through 'a heat exchanger tomaintain the desired tem- .perature and is then introduced intothespinprovide a method for producing high-quality 4s yarns by thedirect wet-spinning of gums of ace-. tone-soluble acetate. Afurtherobject is I or intermittently and sent to the in the provision of aneconomical coagulating 9 V bath especially suited for use in connectionwith W W W the wet spinning of acetone-soluble cellulose ace- 5o by Mema These and other one: wm My invention is further illustrated by thefolclmly new harmful lowing examples. Parts are by weight unless Theseobjects are accomplished by my invenmi tion which, briefly stated,comprises spinning a Example I I Avportion of the acid-enrichedcoagulatlns'solution from the spinning trough is diverted con-f gumofacetone-soluble cellulose acetate contain dl Cellulose acetate gumcontaintng may, eellulose acetate (54.5% combined acetic acid), 78.75%acetic acid, 5.95% water, at a temperature of 295 C., was spun through a240-hole spinneret, hole diameter 0.004 inch, into acoagulating bath of12% acetic acid, 17% ammonium acetate in water at 8 C. Aftercoagulation, the yarn was stretched 21.6% in air, and the yarn collectedin the form of loose coils in a slowly revolving can, washed and dried.v

per denier, dry elongation 34.7%.

Example II The same gum used in Example I was spun into a coagulatingbath of 12% acetic acid, 17% ammonium acetate in water at 8 C. The yarnwas collected in the form of loose coils in a slowlyrevolving can,washed and dried. Denier per filament 20, dry tenacity 0.79 gram perdenier, dry elongation 54.3

Example III Cellulose acetate gum containing 14.35% (54.5% combinedacetic acid) cellulose acetate, 6.85% water, 78.8% acetic acid, Was spunDenier per filament 20, dry tenacity 0.88 gram .through a 1600-holespinneret, hole diameter 0.002 inch, into a coagulating bath of 13.5%acetic acid, 16.3% ammonium acetate in water at 9 C. After coagulation,the yarn was Example v11 1 The same gum used in Example VI was spunthrough a 240-hole spinneret, hole diameter 0.004 inch, into acoagulating bath of 11.9%

acetic acid, 25% ammonium acetate in water at 9 C. The final spinningspeed was 1800 inches per minute. The yarn was collected as loose coilsin a slowly revolving can, washed and dried under substantially notension. Denier per filament 17.5, dry tenacity 0.95 gram per denier,dry elongation 45.6%. I

My invention is, of course, susceptible to wide 7 variation from theexact conditions set out in the foregoing examples, which are forpurposes of illustration only. Thus, any cellulose acetate in theacetone-soluble range having a. combined acetic acid content of 50% to57% may be employed, although the preferred acetate is one containingfrom 54.5% to 56% combined acetic acid.

A gum composition containing 12% to 15% by weight of cellulose acetateis in general preferred but a higher content is permissible if the gumis heated to reduce its viscosity. The water content of the gum shouldnot exceed 15% based on the total weight of the solution, andispreferably maintained within the range of 5-l0%.

The small percentage of sodium, ammonium, cal-- cium, or magnesiumsulfate normally resulting from neutralization of the sulfuric acidacetylation catalyst may be retained, in the gum with- The gum used inExample 111 was spun through a 1500-hole spinneret, hole diameter 0.002inch, intoa coagulating bath of 12.1% acetic acid, 15.1% ammoniumacetate at 9 C. The final spinning speed was 1500 inches per minute. Theyarn was collected asloose coils in a slowly revolving can, washed anddried under substantially no tension. Denier per filament 3.9, drytenacity 0.88 gram per denier, dry elongation 49.7%.

. Example V Ezample VI Cellulose acetate gum containing 14% celluloseacetate (54.5% combined acetic acid), 4.6%

water, 81.4% acetic acid at a temperature of 26 C., was spun through a240-hole spinneret,

The,acetic acidcontent of the coagulating bath should be kept under 15%,and preferably the acid content should be maintained at about 12% byweight. Acetic acid concentrations higher than 15% result in a weak gelyarn and broken filaments. The concentration of the ammonium .salt inthe coagulating bath will depend to a large extent on the denier of theyarn being spun but should not exceed 25% by weight of the bath.

For example, when spinning 3 denier per filament yarn, satisfactoryresults are obtained if hole diameter 0.004 inch, into a coagulationbath of 12.25% acetic acid, 20.7% ammonium acetate at 12 C., at a speedof 1800 inches per minute. The yarn was collected as loose coils in aslowly revolving can, washed and dried under substantially no tension.Denier per filament 23, dry tenacity 0.77 grams per denier, dryelongation 48.4%.

the concentration of ammonium salt is maintained at 11% to 15%. If yarnof 20 denier per filament is being spun, it is desirable to increase theconcentration 01' ammonium salt somewhat, for instance up to 20% or 25%.

It is desirable to maintain the temperature of the coagulating solutionunder 12 0., but not lower than 3 C. Temperatures lower than 3' C.result in a freezing of the gum in the spinneret. This, of course, couldbe eliminated by heating the gum prior to spinning. If the temperatureof the co u ating solution is raised much above 12 C., the rate ofcoagulation is slowed down to a point where the gel yarn is weak withresultingbroken filaments. Best results are obtained when thetemperature of the coagulant is maintained within the range of 6-9 C.

If desired, the yarn may be subjected to substantial stretch as itpasses through the coagulating bath or it may be withdrawn from .thecoagulating bath and stretched up to 25% to 30% in air. If it is desiredto stretch the yarn more than 30%, the yarn may be run through astretching bathcontaining 25% to 35% acetic acid at a temperature of 35C. to 50 C., and then stretched. In this way, it is possible to obtainup to stretch.

I claim:

1. The method of forming filaments, yarns, and

- threads from cellulose acetate which comprises spinning a gum ofacetone-soluble cellulose acetate containing between' 50% and 57%combined acetic acid, said gum containing less than 15% by weight 0!water. into an aqueous calculating solution maintained at a temp'eratureof from about 8 C. to about 12 0.. said coagulating solution consistingof about 12% by weight of acetic acid, from about 11% to about 25% byweight of ammonium salt oi an acid of the group consisting of formic,acetic and nitric acid, and from about 63% to 77% by weight of water,-and with drawing the formed filaments from said bath.

2. The method which comprises spinning a gum consisting of 15.8% byweight of cellulose acetate containing 54.5% of combined acetic acid,78.75% acetic acid andb.95% water into a coagulating bath consisting of12% acetic acid and 17% ammonium acetate in water maintained at sFRANCIS P. nuns.

